Echo arises when audio from a speaker is picked by a microphone situated nearby. When a speaker and a microphone are being used for telecommunication, the echo can be heard by a far-end talker. A near-end talker may be a user of the speaker and the microphone, while a far-end talker is anyone who uses a communication device (e.g., a portable mobile communication device) to communicate with the user of the speaker and microphone. If the echo is not reduced, the far-end talker encounters a difficult and an uncomfortable listening experience, especially because of the delay after which the echo can be heard.
The echo arises when the microphone and the speaker are part of the same device or when the microphone and the speaker are part of different devices but are situated closed to each other. Echo arises even when the microphone and speaker are not situated close to each other, but the audio output of the speaker is received by or is picked up by the microphone. Examples of echo may be found when the follow types of systems are used: a hands-free automobile telecommunication system, a mobile communication device being used in hands-free or speaker mode, a meeting-room speakerphone, a system that uses ceiling speakers or wall speakers along with microphones on a table or along the ground in a room, physical coupling in a communication device (when vibrations of a speaker transfer to the microphone via the casing or housing of the communication device), etc.
In each of these examples, audio from a speaker is received at a microphone. Sometimes, the audio enters the microphone unaltered. This may be referred to as direct acoustic path echo. Sometimes, the audio is altered by the surrounding (e.g., the ambient space) prior to entering the microphone. These alterations include certain frequencies being absorbed by objects (e.g., soft furnishings) or surfaces in the path between the speaker and the microphone. These alterations also include reflections associated with objects, surface, or boundaries encountered in the path between the speaker and the microphone. Sometimes, the path may be an intra-device path, e.g., the path between the speaker and microphone that goes through the device in which the speaker and microphone are located. Sometimes the path may be a path via the housing of the device. Additionally or alternatively, the path may be a path that is situated outside the device regardless of whether or not the speaker and microphone are located in the same device. Therefore, even when the speaker and microphone are located in the same device, audio from the speaker may enter the microphone after traveling on a path situated outside the device.
Therefore, what is needed is a system for echo cancellation, i.e., a system that substantially reduces the echo encountered by the far-end talker.